A significant problem with night-time driving is that the rear view mirrors of the vehicle can reflect the light from headlights of a trailing vehicle into the eyes of the driver, thereby impairing the vision of the driver. A conventional solution to this problem, used primarily with interior, center-mounted rear view mirrors, is to employ a prism mirror with a switch lever on the mirror housing. The switch can be moved between a daytime position, providing direct, normal intensity reflection from the mirror surface, and a night time position providing a reduced intensity reflection. With the intensity of light reflected to the driver, the intensity of reflected headlights from trailing vehicles is insufficient to impair the driver's vision.
Another method proposed for reducing the intensity of light reflected from a rear view mirror is to employ an assembly wherein a reflective member and a transparent member are mounted in a sealed housing with a gap therebetween. A liquid light absorbing medium is disposed between the reflective and transparent members, and this medium, by absorbing a portion of the light transmitted to the reflective member and a portion of the light reflected by the reflective member, reduces the intensity of the light ultimately reflected to the driver. The amount of light reduction depends on the amount of light reducing medium between the transparent and reflective members. The transparent and reflective members may be movable with respect to each other so as to vary the size of the gap therebetween, thereby varying the amount of light reducing medium between the members and the amount of light intensity reduction achieved. That is, when the size of the gap is reduce, light reducing medium is forced out of the gap, and when the gap is enlarged, light reducing medium is drawn into the gap.
Different mechanisms for effecting relative movement between the transparent and reflective members have been proposed in the patent literature. For example, U.S. Pat. No. 3,198,070 discloses a solenoid mechanism and an electromagnet mechanism for moving a mirror within a housing to vary a gap between the mirror and a glass front of the housing. U.S. Pat. No. 3,567,312 discloses a day-night mirror actuation mechanism in which a chamber between a diaphragm and a glass is filled with fluid light controlling medium, and a pressure chamber is disposed within the housing. A spring within the chamber biases the diaphragm, to which the mirror is attached, into a spaced apart position with respect to the glass. When the pressure chamber is evacuated, the spring is compressed and the diaphragm moves forward to press the mirror into the glass. U.S. Pat. No. 3,233,515 discloses a rear view mirror in which a mirror controlling diaphragm is spring biased and is attached to a cable which extends to a driver-accessible control position and is used for manually moving the mirror against the bias of the spring.
A number of references disclose mechanisms whereby a pump is used to force a light attenuating medium between the glass and the mirror. For example, U.S. Pat. No. 3,259,017 discloses a system in which a pump mechanism is used to selectively force a light dimming fluid between the mirror and the glass. U.S. Pat. No. 4,054,374 discloses a mirror attached to a flexible diaphragm. A fluid can be pumped between the mirror and the lens to form a gap therebetween, the mirror being movable on the flexible diaphragm. U.S. Pat. No. 4,726,656 discloses a mirror in which a light attenuating fluid may be forced between the reflector plate and a window plate. A number of different pump mechanisms are disclosed.
The mechanisms described in the forgoing patents are costly, technologically difficult to employ, or otherwise not practical. For these reasons, these mechanisms have met with little, if any, commercial acceptance. Accordingly, a commercial need exists for a dimming mirror assembly that employs simpler and less expensive versions of the mechanisms described in the above-mentioned patents or simpler and less expensive alternatives to the above-mentioned mechanisms.